This invention relates to agricultural irrigation and specifically, to a method and apparatus for forming drip tape or hose for below or above ground drip or trickle irrigation systems.
Drip irrigation hose or tape has been available now for several years. Typically, agricultural drip tapes are formed from relatively thin, flexible, continuous plastic strips folded over and seamed along a longitudinal edge to establish a primary flow path. One or more secondary flow paths are typically formed within the primary flow path by fixing discrete emitter devices along the length of the tape or hose, or by applying parallel strips of plastic material within the hose interior (for example, in the area of the longitudinal edge overlap) to form a secondary flow path. It is generally the case that the primary flow path is connected to the water supply with inlets and outlets to and from the secondary flow path, so that water flows from the primary path to the secondary flow path, and then out of the drip tape in a controlled fashion. Some tape or hose constructions incorporate turbulence inducing regions in the secondary flow path to prevent clogging and reduce the sensitivity of the flow rate to pressure changes.
Drip irrigation hoses or tapes are well represented in the patent literature, and examples may be found in U.S. Pat. Nos. 3,870,236; 3,896,999; 4,009,832; 4,247,051; 4,430,020; 4,473,191; 4,874,132; 4,880,167; 4,984,739; 5,163,622; 5,181,532; 5,203,503; 5,207,386; 5,282,578; and 5,333,793.
Despite the wealth of innovative drip irrigation technology, significant areas of concern remain relating to reliability and cost. For drip tape to be effective and commercially viable, it is essential that the secondary flow path not become clogged with solid matter in the water supply, or by outside debris blocking the outlets. At the same time, to be commercially viable, drip tape must be economical to manufacture.
In commonly owned, co-pending application Ser. No. 08/570,014, filed Dec. 14, 1995, there is disclosed a new and improved drip tape construction which offers advantages not found in the drip tape constructions of which we are presently aware. In the exemplary embodiment, the tape is formed by a strip of flexible PE material folded over and seamed along overlapped longitudinal edges. Interiorly of the tape, and in an area remote from the overlapped seam, there is a pre-formed longitudinally extending plastic bead or strip which defines a series of axially spaced secondary flow paths.
Each secondary flow path has a secondary flow channel including inlet, turbulence inducing, and outlet regions, all of which are preformed on one side of the hot melt bead or strip. The pattern side of the bead is applied face down on the sheet so that the sheet wall itself closes the secondary flow channel except for a plurality of inlets formed in the bead at longitudinally spaced locations along the inlet region. These inlets are arranged perpendicular to the longitudinal axis of the tape, and thus also perpendicular to the secondary flow channel. The inlets are located on both sides of the secondary flow channel, in longitudinally spaced relationship, with the inlets on one side of the secondary flow channel offset longitudinally with respect to the inlets on the opposite side of the secondary flow channel. In this exemplary embodiment, the inlet region extends well over half the total length of the secondary flow path, but this dimensional relationship may vary.
The inlet region leads to a turbulence inducing region formed by a series of peaks and valleys on opposite sides of the secondary flow channel, in longitudinally offset relationship so that the peaks on one side of the secondary flow channel in this region project towards the valleys on the opposite side of the flow channel. The peaks projecting from both sides of the secondary flow channel lie along a line through the center of the secondary flow channel in the exemplary embodiment, thus creating a tortuous path which induces turbulence in the secondary flow path. It is this turbulence that dissipates energy and creates zero or near zero pressure discharge to atmosphere. The turbulence also prevents clogging of the secondary flow path by debris or other solid impurities within the primary water supply.
Downstream of the turbulence inducing region, an outlet region is provided which communicates with an elongated slit in the tape wall which allows the water in the secondary flow path to escape in a controlled drip-like fashion. The outlet region, or reservoir, is otherwise axially closed in the downstream direction, thus isolating the path from the inlet region of the next adjacent downstream secondary flow path, and thus also forcing all water to exit via the elongated slit in the tape wall. In the preferred arrangement, the secondary flow paths are formed of substantially transparent material, for reasons stated in the ""014 application.
In accordance with this invention, a process and related apparatus are disclosed for forming drip tape, similar, but not limited to that described above, in an efficient and reliable manner.
In the exemplary embodiment of this invention, a modular production line is utilized, with the various modules or stations configured to perform certain manufacturing and/or assembly steps within the overall process. Generally, molten material is extruded from an extrusion die in a first module, with the material extruded onto an intermediate one of a vertical calendar stack of three rolls. The invention is not limited, however, to supplying the strip material from an extruder. In this exemplary embodiment, the extrudate travels around and between the two lower rolls in the calendar stack where it is supported, sized, surface finished and thermally stabilized. A thin strip or film, about 3-4xc2xd inches (depending on final drip tape specifications) in width (from 6 to 25 mil in thickness, again depending on final specification) leaves the calendar stack and travels to a second module where the sheet or film is trimmed to a desired width, e.g., about 2.5-3.5 inches. Trimmed scrap may be fed back into the extruder for recycling. In this second module, additional thermal stabilization (i.e., cooling) may take place as required. As the strip or film exits this second module, it may be electronically scanned for impurities or holes, utilizing a conventional scanner.
The sheet or film then progresses to a third module or station where the material is slit at predetermined, longitudinally spaced locations on or adjacent to the longitudinal centerline of the strip, in order to provide outlet openings or vents in the strip wall, one for each secondary flow path. Provisions for thermal management need not be incorporated into this third module but can be if desired and/or needed. A phase adjuster unit is integrated into this module for the purpose of timing the slitting operation with the specific secondary path geometry added at the following module. The pitch or spacing of the slits can be changed at this location by, for example, changing the size of the slitting wheel or by changing the number of slitting knives on the wheel.
The slit film or strip now progresses to a fourth module or station where a second strip or bead is extruded onto a rotating form wheel which has a specific groove geometry etched or engraved on its periphery, the groove geometry corresponding to one or more secondary flow paths. As the form wheel rotates, it brings the extruded bead into contact with a continuous belt which compresses or forces the molten extrudate into the groove configuration on the periphery of the wheel, thus conforming the still molten material to the secondary flow path geometry. The continuous belt then contains or supports the extrudate through a portion of a revolution of the wheel, thus providing time for the extrudate to solidify or cure in the shape created by the geometry of the wheel groove. While the wheel may have a continuous groove geometry (including plural, isolated flow paths) on its periphery in the exemplary embodiment, it is also possible to create discrete grooves corresponding to individual secondary flow paths which could be used to solidify or cure deposits of various material such as thermosets, thermoplastics, rubber, and silicone. This same wheel configuration could also be used to transport preformed emitting devices to a bonding point on the sheet or film. Both the form wheel and the belt may have provisions for thermal management by internal passages or other means. In addition, the tension of the continuous belt may be varied via adjustable rolls which also allow for different sizes of form wheels.
The solidified and now formed bead exits the form wheel groove and travels around one or more additional rolls onto a transfer roll. At this point, the now formed and cooled secondary flow path bead is bonded to the first underlying strip, with the aid of pressure rollers and heat. During the transfer/bonding step, the strip is supported by an upper one of a pair of rolls which may be thermally regulated as well. The pressure applied by the pressure rollers is controlled and adjustable.
After the addition of the second extrudate forming the secondary flow path(s), the film or strip progresses to a fifth station where it is closed or seamed. This is accomplished by wrapping the semi-finished product around a properly sized mandrel and maintaining continuous contact with the mandrel using a series of rollers mounted on movable arms, in combination with a vacuum applied through the mandrel. This results in a seam or overlap along the length of the sheet or film which is held open until a third extrudate in the form of a hot melt adhesive bead is introduced between the layers or overlap in order to enable welding or bonding of the overlapped edges of the sheet or film, to thereby form a continuous water-tight seam along the length of the strip. A pair of nip rolls effect the bonding action using a combination of pressure and thermal management. Additional rolls provide further thermal management as well as a platform for verification of seam closure. It is to be understood that other methods of closure such as sonic welding, thermal impulse welding, laser welding, infrared and heat bonding are viable alternatives which may be incorporated into the process. In addition, butt or nip welding may also be used to close the sheet or film into tubular form.
The seamed tubular drip tape product then progresses through a cooling area or station where it is weaved back and forth as necessary through a series of rollers, providing sufficient time for the finished drip tape to cool prior to packaging. Product codes and product information may be applied on the drip tape exterior at the exit end of the cooling area or in other suitable areas.
Finally, the drip tape is passed to the last station where pull or tension is applied to the drip tape product by a pair of rolls. The pull or tension load is monitored and regulated via a load cell incorporated in the roll drive which assures correct and uniform tension of the product as it exits the production process and moves toward a packaging station. The latter does not form a part of this invention.
Accordingly, the process in accordance with this invention in its broader aspects includes the steps of:
a) supplying a longitudinally continuous strip of flexible plastic material in a first direction;
b) heating a narrow band of the strip continuously along its length;
c) depositing a continuous pre-formed bead of plastic material on an upper surface of the strip, along the narrow band, while the strip moves in the one direction;
d) cooling the strip and the bead;
e) folding the strip longitudinally so that the longitudinal edges overlap; and
f) sealing the longitudinally edges to form a tubular drip tape with a longitudinal, overlapped seam, with the bead extending parallel to the seam and in generally opposed, facing relationship thereto.
In another aspect, the invention relates to a process of forming agricultural drip tape wherein a primary flow path is formed by folding and seaming a continuous length of flexible plastic film along longitudinal edges thereof, and where a secondary flow path is provided on an interior surface of the film prior to folding and seaming, wherein the secondary flow path is formed by:
a) continuously extruding a thin bead of material into a peripheral groove formed in an external surface of a rotating form wheel, the groove having a secondary flow path configuration;
b) confining the bead of material in the peripheral groove for at least part of the circumference of the wheel by engaging the wheel with an endless belt arranged to overlie the groove; and
c) depositing the bead of material on the film along a narrow band of the film.
The apparatus in accordance with the invention broadly includes:
a first supply station adapted to supply a continuous length of flexible material;
a second station including a trimmer roll and a pair of associated knife blades arranged to trim opposite longitudinal edges of the material to form a strip of predetermined width;
a third station including a slitter wheel arranged to cut axially spaced longitudinal slits in the strip;
a fourth station for applying a bead of material onto a surface of the strip as the strip travels about a roll, the fourth station having at least one pressure roller to apply pressure to the bead as it is joined to the surface, the bead having one or more secondary flow paths formed therein, each flow path having an outlet area and wherein drives of the third and fourth stations are coordinated so that each outlet area lies radially adjacent a corresponding one of the longitudinal slits; and
a fifth station including a plurality of rollers arranged to wrap the strip about a mandrel into tubular form; a nozzle arranged to apply an adhesive bead along one of the longitudinal edges of the strip; and at least one pressure roller for.applying pressure along the longitudinal edge to form a bonded seam between the longitudinal edges of the strip.
Other objects and advantages of the subject invention will become apparent from the detailed description which follows.